<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script type="text/javascript">
			// console.log(num); //undefined
			var a = 6;
			var a = 66;

			// console.log(b);
			let b = 9;
			// let b = 6;
			
			for (let i = 0; i < 3; i++) {
				console.log(i);
			}
			console.log(i);
			
			/*
			  1.声明前不能使用
			  2.不允许重写声明
			  3.块级作用域
			*/
		</script>
	</body>
</html>
